FIELD OF THE INVENTION
This invention relates to a nozzle and method. More specifically, it is directed to an improved fluid mixing nozzle that creates chaotic turbulent flow and induces vortices to form in the flow, thereby, transferring energy and velocity from the flow core to the boundary.
Efficient mixing of fluids is crucial for many devices and processes. For example, eductors, or jet pumps, accomplish mixing by contacting an accelerated jet of one fluid with a relatively stationary second fluid. Flow instabilities at the first fluid's boundary layer as well as the reduced pressure within the accelerated fluid causes entrainment of the second fluid.
Prior efforts of improving the mixing include distorting the edge of the nozzle outlet to produce eddies within the flow. The results achieved with the distortions, however, have been relatively ineffective. A second method of increasing the mixing effect includes pulsating the velocity or pressure of the first fluid. However, pulsating the velocity consumes external energy and, therefore, is often inefficient. A third method of enhancing the mixing effect is vortex induction in the jet flow (see U.S. Pat. No 4,519,423 that issued to Ho et al. on May 28, 1985). The swirling vortex promotes both bulk mixing and molecular dispersion.
Eductors often include a diffuser positioned downstream of the nozzle for pressure recovery. Without a diffuser, the flow energy dissipates rapidly. Typical diffusers have an inlet cross sectional area that is less than the outlet cross sectional area. Generally, a diffuser is a flow passage device for reducing the velocity and increasing the static pressure of a fluid. Therefore, the pressure gradient of the fluid opposes the flow. As a consequence, if the walls of the diffuser are too steep, the boundary layer may decelerate and thicken causing boundary layer separation. The separation wherein the flow velocity of the fluid cannot overcome the back pressure, may result in a reverse flow of fluid near the diffuser wall. Diffuser wall separation causes inefficient pressure recovery and inefficient velocity reduction.
One method of preventing diffuser wall separation includes using relatively long diffusers with a small taper angle. However, space or weight limitations may prevent the use of a long diffuser. A second method to prevent diffuser wall separation is to energize the boundary layer by maintaining the energy near the diffuser wall.
Techniques of energizing the boundary wall include active methods and passive methods. An example of an active method is injection of additional fluid near the diffuser wall where stall is likely to occur. In general, passive methods involve transferring energy from the flow core, which has a relatively higher velocity than the boundary portions, to the boundary portions.
In other words, the flow at any particular point in the diffuser has a kinetic energy flux profile. For example, in a typical diffuser, the axial portion has a greater velocity than the boundary portion. Thus, the flux profile is peaked. However, a uniform exit flow profile provides greater pressure recovery; and the maximum pressure recovery is achieved with a peaked inlet profile and a uniform outlet profile. Consequently, transferring energy and velocity from the flow core to boundary portions results in greater pressure recovery.
An effective manner of accomplishing the passive transfer of energy to the boundary portions includes creating vortices within the flow as shown in U.S. Pat. No. 4,971,768 that issued to Ealba et al. on Nov. 20, 1990, U.S. Pat. No. 4,957,242 that issued to Schadow on Sep. 18, 1990, and Ho et al. Generally, Ealba et al. discloses vortex creation using a thin convoluted wall member positioned downstream of the nozzle; Schadow shows vortex creation using a nozzle having an elongated outlet that produces a swirling of the exiting fluid; and Ho et al. reveals vortex creation using a noncircular outlet having unequal major and minor axes, with the major axis to minor axis ratio less than five.
Though the above mentioned nozzles and mixing devices may be helpful in mixing, enhanced entrainment of a secondary fluid, and pressure recovery, they can be improved to provide greater mixing efficiency, greater pressure recovery, higher entrainment vacuum, and to allow for the use of relatively shorter diffusers, thereby, reducing cost and energy consumption. None of the references show creation of a chaotic turbulence and wide scale vortex induction to improve mixing and pressure recovery.